Radiation ray detector and method of manufacturing the detector

ABSTRACT

The light receiving sections of solid-state image sensing devices ( 2   a  and  2   b ) are disposed on a base ( 1 ) to adjoin each other, and are fixed with an adhesive resin ( 11 ). A transparent film ( 3 ) is formed on the light receiving sections so as to wholly cover a gap ( 25 ) and have a flat surface on which a layer of a scintillator ( 4 ) is formed.

TECHNICAL FIELD

[0001] This invention relates to a radiation detector, and, moreparticularly, to a radiation detector constructed by arranging aplurality of image sensors so as to take a radiation image having alarge area, and relates to a method for manufacturing the radiationdetector.

BACKGROUND ART

[0002] An X-ray image sensor using a CCD, in place of an X-rayphotosensitive film, has been widely employed as an X-ray diagnosticinstrument for medical use. In such a radiation imaging system,two-dimensional image data by radiation is obtained as an electricalsignal by use of a radiation detector that has a plurality of pixels,and an X-ray image is displayed on a monitor by processing the signalwith a processor. A typical radiation detector has a configuration inwhich a scintillator is disposed on photodetectors arrangedone-dimensionally or two-dimensionally, and incident radiations aretransformed by the scintillator into light, and are detected.

[0003] In this type of radiation detector, a yield obtained whenmanufactured deteriorates proportionately with the enlargement of animage. As a solution to this problem, a technique is known in which aplurality of detecting elements are arranged to enlarge an image when alarge-screen imaging device for use in taking a chest X ray, forexample, is produced, as disclosed in JP 09-153606A. This publicationmentions that the yield of each element is prevented from decreasing,and production costs are reduced by combining the elements of a lightreceiving screen smaller than an actual imaging screen together.

DISCLOSURE OF THE INVENTION

[0004] However, there is a problem that a scintillator is liable toseparate from a boundary (a joint)with an adjoining detecting elementwhen a plurality of detecting elements are arranged to make a largescreen in this way. This problem causes a concern that the resolution inthe vicinity of the joint will decrease or that the scintillator willcompletely separate therefrom.

[0005] It is therefore an object of the present invention to provide aradiation detector constructed so that the durability of a scintillatorcan be secured, and resolution especially in the vicinity of a joint canbe prevented from decreasing, and to provide a method for manufacturingthe radiation detector.

[0006] In order to achieve the object, the radiation detector accordingto the present invention is characterized by comprising (1) a pluralityof image sensor panels each of which has a substrate and a lightreceiving section formed by two-dimensionally arranging a plurality ofphotoelectric detectors on the substrate in the vicinity of at least oneside of the substrate, (2) a base on which the light receiving sectionsof the image sensor panels are arranged to be adjacent to each other,(3) a surface-flat, transparent film integrally covering the whole ofthe light receiving sections of the plurality of image sensor panels,and (4) a scintillator formed directly on the transparent film. Theradiation detector according to the present invention can have astructure in which, for example, two image sensor panels are connectedto each other, or four image sensor panels are connected to each otherin two-by-two array.

[0007] A method for manufacturing the radiation detector according tothe present invention is characterized by comprising the steps of (1)preparing a plurality of image sensor panels each of which has a lightreceiving section formed by two-dimensionally arranging a plurality ofphotoelectric detectors on a substrate in the vicinity of at least oneside of the substrate, (2) arranging the image sensor panels on a base,so that the light receiving sections are adjacent to each other, (3)forming a surface-flat, transparent film generally covering the surfaceof the whole of the light receiving sections of the image sensor panels,including gaps generated therebetween, and (4) forming a scintillatordirectly on the transparent film.

[0008] Preferably, the scintillator is 100 μm to 1000 μm in thickness.

[0009] Preferably, the gap generated between the image sensor panels is50 μm or less, and the transparent film is 2 μm to 30 μm in thickness.Alternatively, the gap may be 50 μm to 70 μm, and the transparent filmmaybe 5 μm to 30 μm in thickness.

[0010] According to the present invention, a light receiving sectionthat has a large image-pickup area is formed by arranging the lightreceiving sections of the plurality of image sensor panels so as toadjoin each other. A transparent film is wholly formed on the lightreceiving sections while flattening the surface thereof, and ascintillator is formed directly on the film, whereby a uniformscintillator can be formed, and a detector having uniform imageproperties can be obtained. Further, since the scintillator is formed onthe flat film, the scintillator can be effectively prevented fromseparating therefrom.

[0011] Preferably, the image sensor panels have a circuit sectionelectrically connected to the photoelectric detectors. Thus, there is noneed to form another circuit used to read signals, whereby the devicecan be easily manufactured, and the handling thereof can be facilitatedafter the scintillator is formed.

[0012] Preferably, a protective film is further provided to cover thescintillator and hermetically seal it. If the scintillator is made of ahygroscopic material or a low-intensity material, the durability thereofcan be secured by hermetically sealing it with the protective film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a perspective view showing an embodiment of theradiation detector according to the present invention,

[0014]FIG. 2 is a sectional view thereof, and

[0015]FIG. 3 is a partially enlarged view of FIG. 2.

[0016]FIG. 4 to FIG. 8 are views for explaining steps of manufacturingthe detector of FIG. 1, i.e., a method for manufacturing the radiationdetector according to the present invention.

[0017]FIG. 9 is a plan view showing another embodiment of the radiationdetector according to the present invention.

[0018]FIG. 10 and FIG. 11 are plan views, each showing an image sensorpanel used in another embodiment of the radiation detector according tothe present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

[0019] Preferred embodiments of the present invention will hereinafterbe described in detail with reference to the accompanying drawings. Tofacilitate the comprehension of the explanation, the same referencenumerals denote the same parts, where possible, throughout the drawings,and a repeated explanation will be omitted. Additionally, the size andshape of each component in each drawing are not necessarily the same asthe actual ones, and some components are magnified in size and in shapein order to facilitate the understanding thereof.

[0020]FIG. 1 is a perspective view showing an embodiment of theradiation detector according to the present invention, FIG. 2 is asectional view thereof, and FIG. 3 is a partially enlarged view of FIG.2. The radiation detector 100 in this embodiment is formed by disposingsolid-state image sensing devices 2 a to 2 d, which are four imagesensor panels, in 2×2 array on a ceramic base 1. Each of the solid-stateimage sensing devices 2 a to 2 d is fixed to the base 1 with an adhesiveresin 11.

[0021] Each solid-state image sensing device 2 is constructed bytwo-dimensionally arranging photoelectric detectors 21 that perform aphotoelectric conversion on a substrate 20 made of, for example,crystalline Si. The photoelectric detectors 21 are formed out ofphotodiodes (PD) or transistors. The part where the photoelectricdetectors 21 are arranged is hereinafter referred to as a lightreceiving section. Each photoelectric detector 21 is electricallyconnected by a signal line, not shown, to a corresponding electrode pad22 of electrode pads 22 disposed along two adjoining sides of thesolid-state image sensing device 2 through a shift register 23. Thesolid-state image sensing devices 2 a to 2 d are arranged so that thelight receiving sections adjoin each other, in other words, so that theelectrode pads 22 occupy a peripheral part. This arrangement makes itpossible to dispose the light receiving sections of the solid-stateimage sensing devices 2 as close to each other as possible. Further, aninsensible field that cannot obtain an image can be narrowed by makingthe gap between the light receiving sections as small as possible.

[0022] A transparent film 3 that is transparent to light of a wavelengthrange to which the photoelectric detector 21 is sensitive is formed onthe solid-state image sensing devices 2 a to 2 d so as to wholly cover agap 25 adjoining the light receiving sections and between the lightreceiving sections. Preferably, a resin superior in surface smoothnessand excellent in light transmission characteristics, such as a polyimideresin, is used as the transparent film 3. A columnar scintillator 4 bywhich incident radiation is transformed into light of a wavelength rangeto which the photoelectric detector 21 is sensitive is formed on thetransparent film 3. Various materials can be used as the scintillator 4,and, for example, CsI doped with T1 that is superior in luminousefficiency is preferable.

[0023] Further, a protective film 5 is formed with which thescintillator 4 is covered, which extends to the part between theelectrode pad 22 of each solid-state image sensing device 2 and theshift register 23, and with which the scintillator 4 is hermeticallysealed The protective film 5 is radiolucent and is impermeable to watervapor, and, for this film, it is preferable to use, for example, apoly-para-xylylene resin (manufactured by Three Bond Co., Ltd.;registered by Parylene), especially poly-para-chloroxylylene(manufactured by the same company; registered by Parylene C). A coatingfilm of Parylene has excellent properties suitable as the protectivefilm 5, because it is extremely small in permeability to water vapor andgas, is superior in water repellency and in chemical resistance, isexcellent in electric insulation regardless of its thinness, and istransparent to radiation and visible rays.

[0024] Next, referring to FIGS. 4 to 8, a detailed description will begiven of steps of manufacturing the radiation detector, i.e., a methodfor manufacturing the radiation detector according to the presentinvention. Four solid-state image sensing devices 2 structured as shownin FIG. 4 are first prepared. Thereafter, the solid-state image sensingdevices 2 a to 2 d are arranged in two-by-two array on the surface ofthe base 1 having a flat surface, with the light receiving surface ofthe photoelectric detector 21 facing upward, so that the light receivingsections thereof can adjoin each other, in other words, so thatelectrode pads 22 can be disposed outside, and they are fixed onto thebase 1 with an adhesive resin 11 (see FIG. 5).

[0025] Thereafter, polyimide is applied onto the entire light receivingsection (including the gap 25 generated therebetween) while masking thepart of the electrode pads 22, and is hardened, thereby forming thetransparent film 3 having a thickness of about 5 μm (see FIG. 6). Thus,the gap between the solid-state image sensing devices 2 a to 2 d isclosed with the transparent film 3, and, even when there is a differencein level between the surface positions of the elements, the surface ofthe transparent film 3 can be smoothly formed.

[0026] Thereafter, CsI doped with T1 is grown as a columnar crystal ofabout 400 μm in thickness on the thus structured transparent film 3according to the vacuum deposition method, whereby the layer of thescintillator 4 is formed (see FIG. 7). As a result, the layer of thescintillator 4 is formed on the whole light receiving sections of thesolid-state image sensing devices 4 a to 4 d. Since the surface of thetransparent film 3 that serves as a base where the layer of thescintillator 4 is formed is smooth as mentioned above, a uniform layerof the scintillator 4 can be formed over the entire light receivingsections including the gap therebetween.

[0027] CsI has high hygroscopicity and will be dissolved while absorbingthe water vapor of the air if it remains exposed, and therefore, for itsprotection, the whole of the solid-state image sensing devices 2 a to 2d where the scintillator 4 is formed is wrapped together with the base 1with 10 μm-thick Parylene according to the CVD (chemical vapordeposition) method, and the protective film 5 is formed (see FIG. 8).

[0028] In greater detail, coating by vapor deposition is performed in avacuum in the same way as the vacuum deposition of metal, and includes astep of subjecting a diparaxylylene monomer used as a raw material tothermal decomposition, then quickly cooling a resulting product in anorganic solvent such as toluene or benzene, and obtaining diparaxylylenewhich is called diner, a step of subjecting this diner to thermaldecomposition and gathering a stable radical paraxylylene gas, and astep of causing the thus generated gas to be absorbed and polymerizedonto a material so as to form a polyparaxylylene film having a molecularweight of about 500,000 by polymerization.

[0029] There is a gap between the columnar crystals of CsI, and Paryleneenters this narrow gap to some extent, so that the protective film 5comes in firm contact with the layer of the scintillator 4 and seals upthe scintillator 4. The Parylene coating makes it possible to form aprecise thin-film coating, which is uniform in thickness, on the unevenlayer surface of the scintillator 4. Under the CVD method, Parylene canbe formed at a lower vacuum degree than in metal deposition and atnormal temperatures, and can be easily processed.

[0030] Thereafter, the protective film 5 is cut along the part betweenthe electrode pad 22 and the shift register 23, and the outer protectivefilm 5 is peeled off so as to expose the electrode pad 22, whereby theradiation detector 100 shown in FIG. 1 to FIG. 3 is obtained.

[0031] Next, the operation of this embodiment will he described withreference to FIGS. 1 to 3. X rays (radiation) that have entered from anincidence surface pass through the protective film 5, and reach thescintillator 4. The X rays are absorbed by the scintillator 4, and lightof a predetermined wavelength proportional to the quantity of the X raysis emitted. The emitted light passes through the transparent film 3, andreaches the photoelectric detectors 21. In each photoelectric detector21, an electrical signal corresponding to the quantity of the light thathas reached it is generated by a photoelectric conversion, and is storedfor a fixed time. Since the quantity of the light is proportional to thequantity of the incident X rays, the electrical signal stored in eachphotoelectric detector 21 corresponds to the quantity of the incident Xrays, and an Image signal corresponding to an X-ray image can beobtained. The image signals stored in the photoelectric detectors 21 aresuccessively output from each electrode pads 22 through the shiftregister 23 from a signal line not shown, are then transferred outward,and are processed by a predetermined processing circuit, whereby anX-ray image can be displayed on a monitor.

[0032] As described above, according to the present invention, the lightreceiving sections of the solid-state image sensing devices 2 can bedisposed to adjoin each other, and, since the uniform layer of thescintillator 4 is formed on the surface of the light receiving sections,an insensible field generated at a joint between the light receivingsections can be narrowed, and a deterioration in resolution can beprevented. Further, since the light receiving sections, including thejoint therebetween, are covered with the transparent film 3 on which thescintillator 4 is formed, the scintillator 4 can be effectivelyprevented from separating therefrom, and the durability thereof can besecured. Further, since small elements of the light receiving screen arecombined together, the yield for each element can be prevented fromdecreasing greater than a case where large-screen elements aremanufactured, and production costs can be reduced.

[0033] In order to verify the effects that the separation of thescintillator 4 is prevented by filling the gap between the elements withthe transparent film 3, the present inventors prepared four kinds ofpairs of solid-state image sensing devices, and arranged the elements sothat the gap between the elements depends on positions to be occupied bydisposing them so that a gap therebetween is smaller or larger thananother gap. The present inventors then applied polyimide onto thesurface of each pair of elements and hardened it so that each pair formsa transparent film having a predetermined thickness. Thereafter, thepresent inventors deposited CsI of 400 μm as the scintillator 4, andexamined whether the scintillator 4 at a boundary was separated or not.Table 1 shows the result. TABLE 1 Presence off scintillator separationGap Thickness 10 μm 30 μm 50 μm 70 μm 100 μm 1 μm Separated SeparatedSeparated Separated Separated 2 μm Not Not Not Separated Separatedseparated separated separated 5 μm Not Not Not Not Separated separatedseparated separated separated 8 μm Not Not Not Not Separated separatedseparated separated separated

[0034] It was ascertained that the scintillator 4 can be depositedwithout separation by forming a 5 μm-thick transparent film even whenthe gap is 70 μm.

[0035] From this result, the separation of the scintillator can beprevented by setting the thickness of the transparent film at 2 μm ormore when the gap is 50 μm or less, and setting the thickness thereof at5 μm or more when the gap is between 50 μm and 70 μm. Preferably, thethickness of the transparent film is 30 μm or less since an excessivelythick transparent film causes the scattering of an image in thetransparent film and reduces its resolution.

[0036] If the gap reaches a great thickness of 100 μm, the amount oftransparent film that has entered the gap increases, and the transparentfilm produces a slight hollow part in the gap because of a shrinkagecaused when the transparent film is hardened, and, accordingly, thescintillator is separated. Additionally, since a dead space willincrease proportionately with the enlargement of the gap, as small a gapas possible is desirable. From this fact, it is preferable to controlthe gap to be 70 μm or less.

[0037] It is to be noted that the relationship between the size of thegap and the thickness of the transparent film is satisfied by ascintillator falling within the range of 100 μm to 1000 μm in thickness.

[0038]FIG. 9 is a plan view showing a second embodiment of the radiationdetector according to the present invention. As shown in this figure,the solid-state image sensing devices 2 a and 2 b that are two imagesensor panels may be coupled together to manufacture a radiationdetector with a large screen. Further, it is allowable to arrange threeOr more solid-state image sensing devices in a row so as to make a largescreen or arrange them in 2×m array or in m x n array for a largescreen. If the solid-state image sensing devices are arranged in 2×marray (where m is 3 or an integer greater than 3), solid-state imagesensing devices 2′ other than the image pickup elements disposed at atleast four corners are required to have a structure (see FIG. 10) inwhich the light receiving section 21 is disposed up to the boundary ofat least three sides. Additionally, if the solid-state image sensingdevices are arranged in m×n array (where m and n are each an integer of3 or more), solid-state image sensing devices 2″ to be disposed otherthan at the peripheral part are required to have a structure in whichthe light receiving section 21 is placed on its entire surface (see FIG.11). In this situation, it is preferable to dispose the electrode pad onthe back face and read signals by use of a wire passing through the base1.

[0039] In the foregoing description, the protective film 5 is aParylene-made protective film having a single film structure. However,if a reflection film that is a thin film made of metal, such as Al, Ag,or Au, is placed on the surface of the Parylene-made film, an image withhigh brightness can be obtained by returning the light emitted from thescintillator 4 to the photoelectric detector 21. A Parylene film, forexample, maybe applied onto the surface of the metallic thin film forthe protection of the metallic one. When a moisture-proof material isused as the scintillator 4 or when the whole of the device is containedin a moisture-proof protective case, the protective film 5 is notneeded.

[0040] The transparent film in the present invention does not mean atransparent film in the sense of transmitting a visible ray of light,but means that the transparent film has the transmission properties oflight to which the photoelectric detector of the image sensor panel onwhich the transparent film is disposed is sensitive. Therefore, when useis made of, for example, a photoelectric detector sensitive to aspecific wavelength range of visible light, the film is allowed to benontransparent to visible light outside the sensible range, and, whenuse is made of a photoelectric detector sensitive not to visible lightbut to infrared rays, ultraviolet rays, etc., the film is allowed to benontransparent to visible light if sensible light is transmitted. Thefilm is further allowed to be nontransparent to part of a sensiblerange.

INDUSTRIAL APPLICABILITY

[0041] The radiation detector according to the present invention can besuitably used as a radiation detector that take a radiation image for alarge screen.

1. (Amended) A radiation detector comprising: a plurality of imagesensor panels each of which has a substrate and a light receivingsection formed by two-dimensionally arranging a plurality ofphotoelectric detectors on said substrate in the vicinity of at leastone side of said substrate, a base on which the light receiving sectionsof the image sensor panels are arranged to be adjacent to each other, asurface-flat, transparent film integrally covering the whole of thelight receiving sections of the image sensor panels, and a scintillatorformed by vapor deposition directly on said transparent film.
 2. Theradiation detector according to claim 1, wherein the scintillator is 100μm to 1000 μm in thickness. 3 The radiation detector according to claim1 or claim 2, wherein a gap generated between said plurality of imagesensor panels is 50 μm or less, and said transparent film is 2 μm to 30μm in thickness.
 4. The radiation detector according to claim 1 or claim2, wherein a gap generated between said plurality of image sensor panelsis 50 μm to 70 μm, and said transparent film is 5 μm to 30 μm inthickness.
 5. The radiation detector according to any one of claims 1 to4, wherein said image sensor panel has a circuit section electricallyconnected to said photoelectric detectors.
 6. The radiation detectoraccording to any one of claims 1 to 5, wherein the number of saidplurality of image sensor panels is two.
 7. The radiation detectoraccording to any one of claims 1 to 5, wherein the number of saidplurality of image sensor panels is four, and the four image sensorpanels are connected to each other in two-by-two array.
 8. The radiationdetector according to any one of claims 1 to 7, further comprising aprotective film covering said scintillator for sealing.
 9. (Amended) Amethod for manufacturing a radiation detector, the method comprising thesteps of: preparing a plurality of image sensor panels each of which hasa light receiving part formed by two-dimensionally arranging a pluralityof photoelectric detectors on a substrate in the vicinity of at leastone side of said substrate, arranging said image sensor panels on a baseso that the light receiving sections are adjacent to each other, forminga surface-flat, transparent film integrally covering a surface of thewhole of the light receiving sections of the image sensor panels,closing gaps generated therebetween, and forming a scintillator by vapordeposition directly on the transparent film.
 10. The method according toclaim 9, further comprising a step of forming a protective film coveringthe scintillator for sealing.